Reaction products of tris (hydroxyalkyl) isocyanurates, such as tris (2-hydroxyethyl) isocyanurate, and either acrylic or methacrylic acid, exhibit many of the properties needed by photopolymerizable monomers in a dry-film photoresist. For example, these reaction products may be dispersed into a film-forming polymeric binder material to provide a photosensitive layer that has the necessary balance between adhesion to, and removability from, a metal substrate that is to be processed using a photoresist. Further, these reaction products react rapidly upon exposure to an imagewise pattern of actinic radiation to provide an imagewise difference in the removability of the photosensitive layer from the metal substrate. And these reaction products contribute, together with the binder material, to the resistance and continued firm adhesion needed by the developed resist areas of the photosensitive layer during subsequent processing of the resist-covered metal substrate.
However, it has been found that dry-film photoresists that incorporate these monomers have inadequate storage life. After a period of storage of the photoresist, the monomers crystallize, whereupon the photosensitive layer of the photoresist loses the clarity and uniformity needed to achieve the desired rapid and full reaction upon imagewise exposure to actinic radiation, adhesion to substrate, and other desired properties. The result is that despite the unusually desirable combination of other useful properties exhibited by the described monomers, they have limited usefulness in photoresists because of their limited storage life.